(1) Field of the Invention
The present invention relates to a radio terminal and an ad hoc communication method, in particular, in which communication processes are suitably executed automatically when radio terminals having an ad hoc communication function execute ad hoc communication with each other.
(2) Description of the Related Art
By the development of the communication technologies, at present, a communication medium, which is optimal in various communication environments and in using various applications, can be selected by installing a plurality of communication media in single terminal. A wireless LAN (local area network) and cellular dual mode terminal that has been recently released in the market, by installing a wireless LAN communication function in a radio terminal, such as a cellular phone, can switch communication between cellular communication and wireless LAN communication at any time, corresponding to its communication environments. For example, in the office, a call by the VoIP (Voice over Internet Protocol) by utilizing the wireless LAN is executed, and outside the office, a call by utilizing a cellular communication network can be executed.
In this, in the wireless LAN (IEEE (Institute of Electrical and Electronics Engineers) 802.11 Standard), which is installed in the radio terminal, such as the cellular phone, there are two modes of the infrastructure mode and the ad hoc mode. In the case where a user sets the radio terminal to the infrastructure mode, the radio terminal can execute communication via a network by connecting to a nearest access point by wireless. And in the case where the user sets the radio terminal to the ad hoc mode, the radio terminal can directly communicate with a radio terminal that has been set to the ad hoc mode.
Generally, the user sets the radio terminal to the infrastructure mode, and connects the radio terminal to a network in a company or the Internet. However, at the ad hoc mode communication (hereinafter, in some cases, referred to as ad hoc communication), there is a limitation that radio terminals communicating with each other must exist in an area where radio waves can reach both the radio terminals, but there are advantages that the radio terminals can communicate in a state in which an access point does not exist and also communication charges are not necessary because the facilities of the infrastructure are not used. Further, at the ad hoc mode communication, the radio terminals can set a channel for each other, therefore, its communication band can be utilized effectively. Consequently, for example, in the case where a radio terminal that desires to communicate exists in an area where radio waves can reach, it can be supposed that it is effective that the radio terminal executes direct communication by switching the mode to the ad hoc mode.
As technologies relating to the ad hoc communication, there are technologies that have been proposed in the following Patent documents 1 and 2.
In the technology of the Patent document 1, on-demand type communication in which communication terminals move rapidly, two-way communication can be executed for a party being composed of indefinite communication terminals that share topics, and traffic in a network is decreased inside the same group, and the power consumption of the communication terminals is decreased. This is the object of the technology of the Patent document 1. In order to achieve this, when multiple address relay transmission is executed to the indefinite communication terminals, unnecessary communication to communication terminals, which do not have interest or have not existed because of the moving, is prevented.
That is, for each of a plurality of communication terminals that execute group communication, the period of validity, which is longer than going and returning time of communication between the communication terminals being adjacent to each other and is shorter than time supposed to be required for a communication terminal to move out of an area where the communication is available, is set. And the group communication is executed among the communication terminals except the communication terminals whose period of validity has passed.
On the other hand, the technology of the Patent document 2 has an object that a network is formed by asynchronous ad hoc communication. In order to achieve this, a wireless network is formed by the process in which each of radio communication terminals confirms each existence by exchanging management information and also asynchronous communication is executed based on the reception timing described in the management information. With this, without disposing apparatuses becoming control stations such as access points, each of the radio communication terminals can directly communicate with each other in the asynchronous communication. Further, it is not necessary that the information reception be always executed, therefore, the power consumption of each radio communication terminal can be reduced.
[Patent document 1] Japanese Patent Laid-Open (Kokai) 2001-285345
[Patent document 2] Japanese Patent Laid-Open (Kokai) 2003-229869
As conditions that the ad hoc communication is executed between the radio terminals, two conditions are required, that is, as mentioned above, the radio terminals exist in an area where radio waves reach each other (condition 1), and setting information of an ad hoc network is made equal to each other by switching both the radio terminals to the ad hoc mode (condition 2).
In this, the conventional method for executing the ad hoc communication, users of the radio terminals verbally decide the setting information of the ad hoc network beforehand (the condition 1 is satisfied) and the users have executed the setting by inputting the decided setting information in the radio terminals manually (the condition 2 is satisfied). However, executing the setting manually by the users is a very bothersome task for the users. And in this case, since the users decide the setting information verbally, an application for the voice call such as the VoIP is not necessary, and the ad hoc communication has been used only in a limited use such as a file transfer.
And also, in the technologies of the above-mentioned Patent documents 1 and 2, the matching of the setting information for the ad hoc communication of each terminal has been already secured, and each terminal is in a state in which each terminal has already participated or can participate in the ad hoc network. More actually, it is a premise that each terminal is in a state in which the matching of the parameter (the setting information for the ad hoc communication) called as the SSID (Service Set ID) in the management message (beacon message) stipulated in the IEEE 802.11 standard has been secured. Therefore, even in these technologies, it is necessary for each user to input the setting information such as the SSID decided beforehand in the terminal in advance. In this, in the infrastructure mode, the SSID is identification information given to a terminal and an access point being components of the wireless network, and communication cannot be executed when the same SSID is not set in the access point and the terminal.